<template>
  <div class="pagination">
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNumber.start>1" @click="$emit('getPageNo',1)" :class="{active:pageNo==1}">1</button>
    <button v-if="startNumAndEndNumber.start>2">···</button>
    
    <!-- 中间部分 -->
    <button v-for="(page,index) in startNumAndEndNumber.end" :key="index" v-if="page>=startNumAndEndNumber.start" 
      @click="$emit('getPageNo',page)" :class="{active:pageNo==page}">
      {{page}}</button>
    
    <!-- 下 -->
    <button v-if="startNumAndEndNumber.end<totalPage-1">···</button>
    <button v-if="startNumAndEndNumber.end<totalPage" @click="$emit('getPageNo',totalPage)">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>
    
    <button style="margin-left: 30px" :class="{active:pageNo==totalPage}">共 {{total}} 条</button>
    <!-- <h1>{{startNumAndEndNumber}}---{{pageNo}}</h1> -->
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    //父组件传递给字符串的数据：当前页、每一页展示多少条数据、数据总个数、连续页码数
    props:['pageNo','pagesize','total','continues'],
    computed: {
        //计算属性，计算总共多少页
        totalPage() {
            // Math.ceil 向上取整
            return Math.ceil(this.total/this.pagesize);
        },
        //计算出连续的页码起始数字与结束数字[连续的页面数字至少是5]
        startNumAndEndNumber() {
            const {continues,pageNo,totalPage}=this;
            //先定义两个变量存储起始数字与结束数字
            let start =0,end=0;
            //连续页码数字5【就是至少五页】，如果出现不正常的现象【就是不够五页】
            if(continues>totalPage) {
                start=1,
                end=totalPage;
            }else {
                start=pageNo-parseInt(continues/2),
                end=pageNo+parseInt(continues/2);
                // 把出现的不正常现象【start数字出现0|复数】纠正
                if(start <=0) {
                    start=1;
                    end=continues;
                }
                //把出现不正常的现象【end大于总页码】纠正
                if(end>totalPage) {
                    start=totalPage-continues+1;
                    end=totalPage;
                }
            }
            return {start,end};
        }
    },
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }

  .active {
    background: skyblue;
  }
</style>
